1 Gasification coupling power generation process

生物质耦合发电主要有3种方式，直接耦合、气化耦合和蒸汽耦合。直接耦合是研磨过的生物质与燃煤直接在电厂锅炉中混燃的工艺过程；气化耦合则需要设置单独气化炉，生物质气化后将产出的燃气引入电厂锅炉中混燃；生物质在单独设置的锅炉中燃烧，产出的蒸汽并入电厂锅炉蒸汽联箱的工艺则被称为蒸汽耦合。

There are three main ways of biomass coupling power generation: direct coupling, gasification coupling and steam coupling. Direct coupling refers to the process of mixing pulverized biomass and coal directly in the boiler of power plant; For gasification coupling, a separate gasifier needs to be set. After biomass gasification, the produced gas will be introduced into the boiler of the power plant for mixed combustion; The process that biomass is burned in a separately set boiler and the generated steam is incorporated into the steam header of the power plant boiler is called steam coupling.

不同耦合方式工艺特点各异，基于耦合发电技术成熟的欧洲地区的应用情况，对不同耦合方式发电效率及单位投资进行了对比，对比结果如表1所示。

The process characteristics of different coupling modes are different. Based on the application of the mature coupling power generation technology in Europe, the power generation efficiency and unit investment of different coupling modes are compared. The comparison results are shown in Table 1.

从对比数据来看，直接耦合的方式在改造费用及发电效率方面均处于优势地位，但对生物质种类及预处理深度要求较高，容易产生结渣及腐蚀问题，同时也会影响燃煤锅炉的灰渣性质，降低利用价值。蒸汽耦合通过单独设置燃烧锅炉避免了生物质对原有设备的影响，生物质混燃比例仅收到发电汽机制约，但是需要单独增设除尘等净化系统，投资成本将大大增加。气化耦合发电效率与蒸汽耦合接近，但投资成本减少了近1/2，通过气化方式减少了生物质对燃煤锅炉的影响，扩大了可消纳原料的种类，便于灰分的收集及综合利用，同时可以利用现有的空气净化系统达到排放要求，是比较理想的耦合方式。因此，考虑到耦合发电计量问题及政策的倾斜，生物质气化将成为主流的耦合工艺。

From the comparison data, the direct coupling method is in an advantageous position in terms of transformation cost and power generation efficiency, but it has high requirements on biomass type and pretreatment depth, which is easy to cause slagging and corrosion problems, and will also affect the ash properties of coal-fired boilers and reduce the utilization value. The steam coupling avoids the impact of biomass on the original equipment by setting a combustion boiler separately. The proportion of biomass mixed combustion is only limited by the power generation steam turbine, but it needs to add a separate purification system such as dust removal, which will greatly increase the investment cost. The efficiency of gasification coupling power generation is close to that of steam coupling, but the investment cost has been reduced by nearly 1/2. Through gasification, the impact of biomass on coal-fired boilers has been reduced, the types of consumable raw materials have been expanded, which is convenient for the collection and comprehensive utilization of ash, and the existing air purification system can be used to meet the emission requirements, which is an ideal coupling method. Therefore, biomass gasification will become the mainstream coupling process in consideration of the coupling power generation metering problem and the inclination of national policies.

2生物质气化炉技术比较

2 Comparison of biomass gasifier technologies

生物质气化反应需要在气化炉内完成，根据气固接触方式的不同，生物质气化炉主要分为固定床（上吸式、下吸式）、流化床（鼓泡流化床、循环流化床）和气流床；根据运行压力不同可分为常压、加压气化炉。气流床对生物质粒径要求较高（颗粒＜3mm），并不适用于大规模的生物质处理过程，因此，现行的生物质气化技术一般是固定床及流化床2种类型。固定床及流化床气化炉结构的差异影响了其处理规模，燃气特性及品质，从而决定了不同炉型的应用场合。

The biomass gasification reaction needs to be completed in the gasifier. According to the different gas-solid contact modes, the biomass gasifier is mainly divided into fixed bed (upper suction type, lower suction type), fluidized bed (bubbling fluidized bed, circulating fluidized bed) and entrained flow bed; It can be divided into atmospheric and pressurized gasifiers according to different operating pressures. The entrained flow bed has a high requirement on the particle size of biomass (particles<3mm) and is not suitable for large-scale biomass treatment process. Therefore, the current biomass gasification technology is generally fixed bed and fluidized bed. The difference between the structure of fixed bed gasifier and fluidized bed gasifier affects its treatment scale, gas characteristics and quality, thus determining the application occasions of different types of gasifiers.

（1）不同气化炉型适用规模。固定床气化炉内部混合程度及热传导都比较差，导致难以达到同一截面物料分布、温度分布、燃气组成均匀一致，随着尺寸放大，上述问题将更加严重。相对而言，流化床气化炉虽然对原料的尺寸要求更加严格，但其物料及温度均匀性更好，运行较为稳定，在处理规模上更具优势。在正常操作条件下，以常规秸秆为原料的不同气化炉处理能力如图1所示。由图1可知，常压流化床气化炉的处理能力可达100MW左右（约600t/d），而固定床气化炉的处理能力不超过10MW（约60t/d）。由于耦合发电需要达到一定规模才具有较高的经济效益，因此，具有更大处理能力的流化床气化炉将更具优势[3]。

(1) Applicable scale of different gasifier types. The mixing degree and heat conduction in the fixed bed gasifier are relatively poor, which makes it difficult to achieve uniform material distribution, temperature distribution and gas composition in the same section. The above problems will become more serious with the size enlargement. Relatively speaking, the fluidized bed gasifier has more strict requirements on the size of raw materials, but its material and temperature uniformity is better, its operation is more stable, and it has more advantages in the treatment scale. Under normal operating conditions, the processing capacity of different gasifiers using conventional straw as raw material is shown in Figure 1. It can be seen from Figure 1 that the processing capacity of the atmospheric fluidized bed gasifier can reach about 100MW (about 600t/d), while the processing capacity of the fixed-bed gasifier does not exceed 10MW (about 60t/d). Since the coupled power generation needs to reach a certain scale to have higher economic benefits, the fluidized bed gasifier with greater processing capacity will have more advantages [3].

（2）不同气化炉型焦油产量。生物质气化往往伴随着焦油的产生，造成能源浪费的同时还降低了气化效率，还影响了气化设备的稳定运转，不经净化的生物质燃气还会对后续管路及燃烧设备造成严重危害。

(2) Tar output of different gasifiers. Biomass gasification is often accompanied by tar production, which causes energy waste, reduces gasification efficiency, and affects the stable operation of gasification equipment. Unpurified biomass gas will also cause serious harm to subsequent pipelines and combustion equipment.

不同气化炉由于结构不同，其焦油产生量有比较大的差别，其中上吸式固定床气化燃气由于经过低温区域而无法完全裂解，焦油含量高；下吸式固定床气化燃气则可以保证充分的热解温度，焦油含量少，鼓泡式及循环流化床气化炉介于以上2者之间，具体数据见表2[4，6]。

Due to the different structures of different gasifiers, the tar production is quite different, among which the gas from the updraft fixed-bed gasifier cannot be completely cracked because it passes through the low temperature zone, and the tar content is the highest; The downdraft fixed-bed gasification gas can ensure sufficient pyrolysis temperature, with the minimum tar content, and the bubbling and circulating fluidized bed gasifiers are between the above two. See Table 2 [4, 6] for specific data.

（3）不同气化炉型燃气成分。生物质燃气成分是决定燃气热值及燃烧性能的关键因素，理想的燃气组分可以保证更高的耦合发电参数。在气化剂选用空气的条件下，不同类型气化炉产出燃气组成如表3所示。

(3) Gas composition of different gasifier types. The composition of biomass gas is the key factor to determine the calorific value and combustion performance of the gas. The ideal gas composition can ensure higher coupling power generation parameters. Under the condition that air is selected as gasifier, the composition of gas produced by different types of gasifiers is shown in Table 3.

可以看出，固定床与流化床气化炉燃气热值相差不大都具有较高的气化效率，但由于流化床内部温度、物料分布更均匀，产气量、燃气成分相对稳定，其燃气的品质更高[4，6]。

It can be seen that the fixed bed gasifier and the fluidized bed gasifier have relatively high gasification efficiency due to the difference in gas calorific value, but because the temperature and material distribution inside the fluidized bed are more uniform, the gas production and gas composition are relatively stable, and the gas quality is higher [4, 6].

（4）气化耦合发电炉型选择。固定床气化炉由于其自身的种种局限性，不适于用于燃煤电厂生物质耦合发电项目。，固定床气化炉规模较小（一般＜10MW），无法产生规模效应，限制了项目盈利的可能。其次，固定床气化炉下料过程易产生搭桥现象而控制困难，因此燃气品质波动较大，影响了锅炉的运行。处理规模相对较大的上吸式固定床因出口燃气温度较低（约450℃左右）且波动较大，燃气内焦油含量高，在输送过程中存在堵塞管道的风险，也不适用于耦合发电过程。固定床气化炉更加适用于生物质处理规模较小的情况，其中上吸式固定床比较适用于粗燃气不需冷却及净化的场合，比如直接作为小型锅炉或加热炉的燃料或向系统提供工艺热源；下吸式气化炉由于产出焦油含量较低，可以较好的和内燃机联合工作，适用于1MW以下的分布式气化发电。

(4) Selection of gasification coupling power generation furnace type. Due to its own limitations, fixed bed gasifiers are not suitable for biomass coupling power generation projects in coal-fired power plants. First of all, the fixed bed gasifier has a small scale (generally<10MW) and cannot produce scale effect, which limits the possibility of project profit. Secondly, the feeding process of fixed bed gasifier is easy to produce bridging phenomenon and difficult to control, so the gas quality fluctuates greatly, affecting the safe operation of the boiler. The up-suction fixed bed with relatively large treatment scale is not suitable for the coupled power generation process because of its low outlet gas temperature (about 450 ℃) and large fluctuation, and high tar content in the gas. The fixed-bed gasifier is more suitable for the small scale of biomass treatment, in which the up-suction fixed-bed is more suitable for the occasions where the crude gas does not need to be cooled and purified, such as directly serving as fuel for small boilers or heating furnaces or providing process heat source for the system; The downdraft gasifier can work well with the internal combustion engine due to its low tar content, and is suitable for distributed gasification power generation under 1MW.

根据国内气化耦合运行情况估算，耦合发电需要达到一定规模才具有较高的经济效益，折算机组发电容量少约15MW以上。同时为降低对锅炉燃烧的影响，气化燃气的热值、气量也应具有较高的稳定性。流化床气化炉由于其良好的混合效果，均匀的温度分布，稳定的运行效果，更适用于燃煤电厂气化耦合发电、较大规模气化发电、气化合成气制备高附加值生物燃料等场合，也适用于中小城镇生物质（含垃圾）气化供热等。因此，针对燃煤电厂生物质耦合发电项目，适宜采用运行稳定性高的流化床气化炉技术，尤其是负荷灵活度更高，原料混合更均匀的循环流化床。

According to the estimation of domestic gasification coupling operation, the coupling power generation needs to reach a certain scale to have high economic benefits, and the converted unit power generation capacity is at least about 15 MW. At the same time, in order to reduce the impact on boiler combustion, the calorific value and gas volume of gasification gas should also have high stability. Due to its good mixing effect, uniform temperature distribution and stable operation effect, the fluidized bed gasifier is more suitable for coal-fired power plant gasification coupling power generation, large-scale gasification power generation, gasification of synthetic gas to produce high value-added biofuel and other occasions, and also suitable for small and medium-sized cities and towns biomass (including garbage) gasification heating. Therefore, for the biomass coupling power generation project of coal-fired power plant, it is most suitable to adopt the fluidized bed gasifier technology with high operation stability, especially the circulating fluidized bed with higher load flexibility and more uniform raw material mixing.

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